The present invention broadly relates to control mechanisms and, more specifically, pertains to a new and improved construction of a control mechanism for the inlet guide vanes or stator vanes of an axial turbine device or machine having a housing and comprising an axial control sleeve arranged within the housing and translating axially for controlling the stator vanes and a control yoke for axially translating the axial control sleeve and having a pivot shaft pivotably journaled at the housing and arms pivotably journaled at the axial control sleeve.
Generally speaking, the control mechanism of the present invention is intended for the inlet guide vanes or stator vanes of an axial turbine device or machine with a control sleeve arranged in the interior of the machine housing and whose translation in the axial direction controls the inlet guide vanes or stator vanes, the axial translation of the control sleeve being actuated by a control yoke whose pivot axis is pivotably journaled in the machine housing and whose arms are pivotably journaled in the control sleeve.
Such control mechanisms are known, for instance from the Swiss Pat. No. 364,581, patented Sept. 30, 1962, or the German Patent Publication No. 3,125,639, published Jan. 13, 1983 and the cognate aforementioned copending U.S. application Ser. No. 388,231 and serve for the control or adjustment of the inlet guide vanes or stator vanes of, for instance, turbo-compressors, expansion turbines or gas turbine engines. A translation of the control sleeve in the axial direction effects a rotation of the guide vanes or stator vanes about their axis.
Due to the differential thermal expansion of the control sleeve and the machine housing, the support of the control sleeve in the machine housing is difficult to accomplish. The support of the control sleeve described in German Pat. No. 2,235,154, granted Aug. 14, 1974 and the corresponding U.S. Pat. No. 3,829,234, granted Aug. 13, 1974 by means of guide rods comprising two longitudinal positioning rods on one side and two supports permitting horizontal sliding on the opposing side represents a usable solution, particularly for relatively long control sleeves. However, in shorter control sleeves, friction forces of sometimes considerable magnitude arise when the control force does not act precisely in the center of the control sleeve, as is always more or less the case in practice.
The friction forces generated by the corresponding rotating or tipping moment in the supports become larger the shorter is the longitudinal spacing of the supports of the control sleeve. Additionally, when turning the inlet guide vanes or stator vanes, a torsional moment is applied to the control sleeve which leads to considerable sliding friction in a linear guide means of known type. These frictional forces are considerable, especially in turbo-machinery operating with hot gases, and can lead to self-locking or jamming.
As a consequence of the high temperatures, the choice of materials for the components sliding upon one another is limited and coefficients of friction of up to five times the normal value must be expected. It is therefore desirable, especially for hot gas machinery, such as turbines or expansion turbines, to have control sleeve supports offering low frictional resistance.